1. Field of the Invention
The present invention relates to a motor drive control device for an electric power-assisted vehicle such as a bicycle with a motor.
2. Description of Related Art
Power transmission systems of an electric power-assisted vehicle such as a bicycle with a motor include various configurations shown in FIGS. 1 to 6. In the figures, OWC represents a one-way clutch, and a reduction gear may or may not be provided depending on the motor torque and speed characteristics. R gear represents a rear gear, and F gear represents a front gear. The chain is an example, and the same effect can be achieved when other appropriate parts such as a rotary shaft are used.
A difference between an example that uses a variable transmission (FIG. 1) and an example that uses an external gear shifter (FIG. 2) is illustrated only with the first power transmission system in FIGS. 1 and 2. As seen from the comparison between FIG. 1 and FIG. 2, the only difference between the system with the variable transmission and the system with the external gear shifter is that the gear shifter and the OWC are replaced with each other. Therefore, for other power transmission systems, configurations with a variable transmission will only be shown.
In the first power transmission system shown in FIGS. 1 and 2, the front wheel motor drives the front wheel on the ground through no OWC, and an electromagnetic (regenerative) brake can be used. However, even when pedals are not rotated, load is constantly applied by the motor, which increases a constant loss. Also, when the battery is out of charge, the vehicle including such motor load needs to be driven by human power.
On the other hand, respective configurations of the second power transmission system (FIG. 3) to the fifth power transmission system (FIG. 6) are provided with an OWC in a drive route from the motor to the ground. This OWC is either independently provided, or is shared with the pedals. Therefore, when the pedals are not rotated, the motor load does not affect the driving.
In cases of the second and third power transmission systems (FIGS. 3 and 4), the OWC is shared between the motor and the pedals, and because the pedals and the motor are constantly in mechanical synchronization, the OWC is locked and unlocked by a manual pedal operation. Therefore, uncomfortable feeling or a shock to the motor is not caused by the OWC upon locking.
In the fourth power transmission system (FIG. 5), the OWC is provided between the motor and the front wheel, and another OWC is independently provided between the pedals and the rear wheel. In the fifth power transmission system (FIG. 6), both the motor and the pedals drive the rear wheel, but the OWC for the motor and the OWC for the pedals are provided independently from each other.
As described above, in the fourth and fifth power transmission systems, not only an assist operation by the motor is possible, but also the vehicle can be driven by the motor alone, which achieves a function of an electric motorcycle. However, in the aspect of the assist operation, because the motor and the pedals are not mechanically synchronized, when a manual operation to lock and unlock the OWC and a motor operation to lock and unlock the OWC do not occur at the same time, shock and noise are possibly caused. Such a shock results in wear and damage of the motor and the reduction gear.
A conventional technique discloses a control method for a bicycle with an electric motor including one-way clutches respectively provided for the pedals and for the motor and another one-way clutch to be shared between pedals and motor. In this control method, when a force on the pedal is substantially zero, the electric motor is maintained at a no-load rotational speed that corresponds to a vehicle speed at that time, and when the force on the pedal is not substantially zero, the driving force of the motor is controlled in accordance with the force on the pedal. In this conventional technique, the actual vehicle speed is measured, and the motor rotational speed is maintained at a no-load rotational speed that corresponds to the vehicle speed. This makes it possible to prevent a delay in an assist operation when it is needed.
However, this conventional technique can be interpreted to substantially describe only the technical matters that are necessary to maintain a voltage for a no-load rotational speed that corresponds to a vehicle speed. That is, in such a state, a driving force (i.e., torque) is not controlled at all. More specifically, it can be interpreted that the above disclosure describes a system in which a desired rotational speed can be obtained by the internal feedback effect, which is, when outputting a driving voltage that corresponds to a no-load rotational speed, a difference between the driving voltage and a back electromotive force in the motor causes an internal current to flow in proportion to the coil resistance, thereby generating torque. With this configuration, it is not possible to ensure that an appropriate motor drive control is conducted in accordance with a pedaling operation of the rider. Also, because an object of the disclosure is to prevent a delay in assist operation, the disclosure does not provide a solution to the problem of a gap between timing of locking and unlocking the OWC by the pedals and timing of locking and unlocking the OWC by the motor.